Methods of treating subterranean zones penetrated by well bores

ABSTRACT

The present invention provides methods of treating subterranean zones penetrated by well bores in primary well cementing operations, well completion operations, production stimulation treatments and the like. The methods are basically comprised of introducing into the subterranean zone an aqueous well treating fluid comprised of water and a water soluble polymer complex fluid loss control additive.

Cross-References To Related Applications

[0001] This application claims the benefit of Provisional ApplicationNo. 60/284,043 entitled “Water Soluble Polymer Complexes” filed on Apr.16, 2001

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to methods of treating subterraneanzones penetrated by well bores with aqueous treating fluids comprised ofwater and a water soluble fluid loss additive comprised of a polymercomplex.

[0004] 2. Description of the Prior Art

[0005] Well treating fluids are used in a variety of operations andtreatments in oil and gas wells. Such operations and treatments includewell completion operations such as gravel packing to prevent formationsolids from being carried out of the well bore with produced hydrocarbonfluids. In gravel packing, suspended gravel particles are carried into asubterranean zone containing a screen in which a gravel pack is to beplaced by a viscous gelled treating fluid. Once the gravel pack isplaced in the zone, the viscous gelled fluid is broken (the viscosity isreduced) and recovered (returned to the surface). In order to preventthe loss of fluid components of the treating fluid into permeableformations penetrated by the well bore, a fluid loss control additive isincluded in the treating fluid. The gravel pack formed in the well borefunctions as a filter to separate formation solids from produced fluidswhile permitting the produced fluids to flow into and through the wellbore.

[0006] Aqueous well treating fluids containing hydraulic cement areutilized extensively in the construction and repair of oil and gaswells. For example, hydraulic cement compositions are used in primarywell cementing operations which involve the placement of a cementcomposition into the annular space between the walls of a well bore andthe exterior surfaces of a pipe string such as casing disposed therein.The cement composition is permitted to set in the annular space therebyforming an annular sheath of hardened impermeable cement therein. Theobjective of the cement sheath is to physically support and position thepipe string in the well bore and bond the pipe string to the walls ofthe well bore whereby the undesirable migration of formation fluidsbetween subterranean zones penetrated by the well bore is prevented.

[0007] An example of a production stimulation treatment utilizing a welltreating fluid is hydraulic fracturing. That is, a viscous gelledaqueous treating fluid, referred to in the art as a fracturing fluid, ispumped through the well bore into a subterranean zone to be stimulatedat a rate and pressure such that fractures are formed and extended intothe subterranean zone. The fracturing fluid also carries particulateproppant material, e.g., sand, into the fractures. The proppant materialis suspended in the viscous fracturing fluid so that the proppantmaterial is deposited in the fractures when the viscous fracturing fluidis broken and recovered. The proppant material functions to prevent theformed fractures from closing whereby conductive channels are formedthrough which production fluids can flow to the well bore. In order toprevent the loss of the fracturing fluid to permeable subterraneanformations, a water soluble fluid loss control additive is included inthe fracturing fluid. After the viscous fracturing fluid has been pumpedinto a subterranean zone in a formation and fracturing of the zone hastaken place, the fracturing fluid is removed from the formation to allowproduced hydrocarbons to flow through the created fractures. Generally,the removal of the viscous fracturing fluid is accomplished byconverting the fracturing fluid into a low viscosity fluid. This isaccomplished by adding a delayed breaker, i.e., a viscosity reducingadditive, to the fracturing fluid prior to pumping it into thesubterranean zone to be fractured.

[0008] The success of gravel packing operations, primary cementingoperations, fracturing operations and other operations utilizing aqueouswell treating fluids depend, at least in part, on the ability of thetreating fluid used to retain water until it has been placed in adesired well location. That is, as an aqueous treating fluid is pumpedthrough the well bore and contacts permeable subterranean formationspenetrated thereby, water included in the treating fluid can be lost tothe permeable formations. The loss of water from the treating fluid canprevent the treating fluid from functioning in the manner intended. Forexample, when portions of the water forming a cement composition arelost, the consistency of the cement composition is also lost which canprevent the composition from being placed in the intended location, thecomposition can become too viscous for placement and/or the compositionfractures subterranean formations whereby all or part of the compositionis lost. While lightweight foamed aqueous treating fluids such as foamedcement compositions are often utilized, such foamed treating fluids arealso subject to fluid loss when in contact with permeable surfaces.

[0009] Heretofore, a variety of fluid loss reducing additives have beendeveloped and used in aqueous well treating fluids. Such additivesreduce the loss of liquids, usually water, from such treating fluidswhen the treating fluids are in contact with permeable surfaces. Whilethe heretofore utilized fluid loss control additives have achievedvarying degrees of success, there is a continuing need for improvedfluid loss control additives which can be utilized in non-foamed andfoamed aqueous well treating fluids and which effectively reduce fluidloss from the aqueous well treating fluids at high temperatures.

SUMMARY OF THE INVENTION

[0010] The present invention provides improved methods of treatingsubterranean zones penetrated by well bores with aqueous well treatingfluids having improved low fluid loss properties which meet the needsdescribed above and overcome the shortcomings of the prior art.

[0011] The improved methods of this invention for treating asubterranean zone penetrated by a well bore comprise introducing intothe subterranean zone an aqueous well treating fluid comprised of waterand a water soluble polymer complex fluid loss control additive. Thefluid loss control additive is comprised of a polymer complex of two ormore water-soluble polymers. That is, the fluid loss control additivesutilized in accordance with this invention are polymer complexescomprised of a cationic, anionic or amphoteric polymer formed in thepresence of a nonionic polymer. The polymer complexes are comprised ofpolymers which are not physically blended, but which are intimatelyintermixed or interjacent because of the way they are produced. Thefluid loss control additive polymer complexes are produced by formingone of the polymeric components in the presence of another polymericcomponent which is already in place in the polymerization zone. Thus, asolution, emulsion or other preparation of the monomers desired to beincorporated in the formed polymer is prepared with the desiredinitiator or catalyst and a polymer is formed (synthesized) in thepresence of a previously prepared or natural polymer, which is hereinreferred to as the host polymer. Because the host polymer is presentthroughout the polymerization mix, the newly formed polymer isinterjacent with the host polymer. Since both the polymers of thepolymer complex formed are water soluble, the polymer complex is watersoluble.

[0012] The nonionic polymer, i.e., the host polymer, in the fluid losscontrol additive utilized in accordance with the present invention ispreferably a natural polymer. More preferably, the nonionic polymer is ahydroxyalkylated natural gum, and most preferably, the nonionic polymeris ethoxylated hydroxyethylcellulose. The cationic, anionic oramphoteric polymer which is polymerized in the presence of the nonionicpolymer is preferably comprised, at least in part, of monomer unitsderived from a sulfonic acid functional monomer. Most preferably, thepolymer is comprised of 2-acrylamido-2-methyl propane sulfonic acidmonomer units which are present in the polymer in an amount in the rangeof from about 25 mole % to about 75 mole %. The polymer can includeother monomer units such as N,N-dimethylacrylamide, acrylamide, acrylicacid and vinylpyrrolidone.

[0013] A preferred method of this invention for treating a subterraneanzone penetrated by a well bore comprises introducing into thesubterranean zone an aqueous well treating fluid comprised of water anda water soluble polymer complex fluid loss control additive comprised of1 part by weight of a polymer comprising 70 mole % of2-acrylamido-2-methyl propane sulfonic acid, 17 mole % ofN,N-dimethylacrylamide and 13 mole % of acrylamide, and 2 parts byweight hydroxyethylcellulose having 1.5 moles of ethylene oxidesubstitution.

[0014] Another preferred water soluble polymer complex fluid losscontrol additive for use in accordance with the methods of thisinvention is comprised of 1 part by weight of a polymer comprising 40mole % of 2-acrylamido-2-methyl propane sulfonic acid, 30 mole % ofacrylamide, 20 mole % of acrylic acid and 10 mole % of vinylpyrrolidone,and 1 part by weight of hydroxyethylcellulose having 1.5 moles ofethylene oxide substitution.

[0015] The aqueous well treating fluid can be a foamed or non-foamedhydraulic cement composition, a viscous gravel pack forming fluid, afracturing fluid or other aqueous well treating fluid.

[0016] The objects, features and advantages of this invention will bereadily apparent to those skilled in the art upon a reading of thedescription of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] The present invention provides improved methods of treatingsubterranean zones penetrated by well bores utilizing treating fluidscontaining water soluble polymer complex fluid loss control additives.That is, the treating fluids are basically comprised of water and apolymer complex fluid loss control additive and may include hydrauliccement, viscosity increasing gelling agents, cross-linkers for thegelling agents, viscosity breakers and other components known to thoseskilled in the art. Thus, the treating fluids useful in accordance withthe methods of this invention can be compositions basically comprised ofwater and the polymer complex fluid loss control additive, hydrauliccement compositions, gravel pack forming compositions, fracturing fluidsand the like. When the treating fluid is comprised of water and thefluid loss control additive, the fluid loss control additive is presentin an amount in the range of from about 0.09% to about 2.5% by weight ofthe water.

[0018] The water soluble polymer complex fluid loss control additivesuseful in accordance with this invention are comprised of a complex oftwo water soluble polymers. The polymer complexes are prepared bypolymerizing one or more polymerizable monomers in the presence of apreviously formed or natural polymer. The polymer complexes areintercalated as a result of the way they are produced. That is, thecomplexes are prepared by polymerizing monomer components in thepresence of a previously formed or natural polymer which is included inthe polymerization mixture. A solution, emulsion or other preparation ofthe monomers to be polymerized is prepared with the desired initiator orcatalyst and a polymer is synthesized in the presence of the previouslyformed or natural polymer, i.e., the host polymer. Because the hostpolymer is present throughout the polymerization mixture, the hostpolymer is intercalated with the new polymer being formed. Both of thepolymers are water soluble which makes the polymer complex watersoluble. In oil and gas well completion and production stimulationapplications, the polymer complex fluid loss control additives areformed by polymerizing a cationic, anionic or amphoteric polymer in thepresence of a nonionic host polymer. Thus, the term “polymer complexfluid loss control additive” is used herein to mean a cationic, anionicor amphoteric polymer which is polymerized in the presence of a nonionichost polymer.

[0019] As mentioned above, the polymer complex fluid loss controladditives are particularly suitable for use in treating fluids which arebasically comprised of water and other components such as hydrauliccement, viscosity increasing gelling agents or the like. Stated anotherway, the polymer complex fluid loss control additives are particularlysuitable for use in aqueous well treating fluids such as foamed ornonfoamed hydraulic cement compositions, viscous aqueous fracturingfluids and other aqueous well treating fluids utilized in the drilling,completion and stimulation of oil and gas wells.

[0020] The polymer complex fluid loss control additives useful inaccordance with this invention are particularly suitable for use infoamed or nonfoamed hydraulic cement compositions which are utilized forcementing well bores at high temperatures, i.e., temperatures in therange of from about 80° F. to the bottom hole circulation temperature(BHCT), i.e., about 350° F. The polymer complexes provide fluid losscontrol over a wide range of temperature and other well conditions.

[0021] As mentioned, the polymer complexes of the present invention areformed by polymerizing one or more monomers in the presence of a hostpolymer. The host polymer can be a synthetic polymer such as thoseproduced by free radical polymerization or condensation polymerizationor it may be a natural polymer such as a natural gum, a starch, amodified starch, a cellulosic material or a modified cellulosicmaterial. Examples of host polymers that can be utilized in the polymercomplex include, but are not limited to, vinyl polymers, polyolefins,polyacrylates, polyamides, polyesters, polyurethanes, xanthan gums,sodium alginates, galactomannans, carragenan, gum arabic, cellulose andits derivatives, starch and its derivatives, guar and its derivatives,silicone containing polymers and their derivatives, polysiloxanes andtheir derivatives and proteins and their derivatives.

[0022] The host polymer is preferably a nonionic polymer such as a watersoluble natural gum. While various natural gums can be used of the typesdescribed above, a hydroxyalkylated natural gum such as hydroxyethylguar gum or hydroxypropyl guar gum.

[0023] The cationic, anionic or amphoteric polymer formed in thepresence of the nonionic host polymer can include monomer units derivedfrom one or more monomers. Preferably, a majority of the monomer unitsfor forming the polymer are monomer units derived from a sulfonic acidfunctional monomer. Of the various sulfonic acid functional monomersthat can be used, 2-acrylamido-2-methyl propane sulfonic acid monomerunits present in the polymer in an amount in the range of from about 25mole % to about 75 mole % are preferred. One or more additional monomerunits can be included in the formed polymer in addition to the sulfonicacid functional monomer units. Preferred such additional monomer unitsare N,N-dimethylacrylamide monomer units present in the polymer in anamount in the range of from about 10 mole % to about 40 mole %,acrylamide monomer units present in the polymer in an amount in therange of from about 10 mole % to about 30 mole %, acrylic acid monomerunits present in the polymer in an amount in the range of from about 10mole % to about 20 mole % and/or vinylpyrrolidone monomer units presentin the polymer in an amount in the range of from about 5 mole % to about20 mole %.

[0024] A particularly suitable water soluble polymer complex fluid losscontrol additive for use in accordance with this invention is comprisedof 1 part by weight of a polymer comprised of about 70 mole % of2-acrylamido-2-methyl propane sulfonic acid, about 17 mole % ofN,N-dimethylacrylamide and about 13 mole % of acrylamide, and 2 parts byweight of hydroxyethylcellulose having 1.5 moles of ethylene oxidesubstitution.

[0025] Another particularly preferred water soluble polymer complexfluid loss control additive for use in accordance with this invention iscomprised of 1 part by weight of a polymer comprised of about 40 mole %of 2-acrylamido-2-methyl propane sulfonic acid, about 30 mole % ofacrylamide, about 20 mole % of acrylic acid and about 10 mole % of vinylpyrrolidone, and 1 part by weight of hydroxyethylcellulose having 1.5moles of ethylene oxide substitution.

[0026] A method of this invention for cementing a subterranean zonepenetrated by a well bore comprises introducing into the subterraneanzone a cement composition comprised of a hydraulic cement slurried withwater present in an amount in the range of from about 35% to about 50%by weight of cement in the composition and a water soluble polymercomplex fluid loss control additive present in an amount in the range offrom about 0.25% to about 5% by weight of cement in the composition.

[0027] Another method of this invention for cementing a subterraneanzone penetrated by a well bore comprises introducing into thesubterranean zone a cement composition comprised of a hydraulic cementslurried with water present in an amount in the range of from about 35%to about 50% by weight of cement in the composition, a water solublepolymer complex fluid loss control additive present in an amount in therange of from about 0.25% to about 5% by weight of cement in thecomposition, a gas present in an amount sufficient to foam the aqueouswell treating fluid and a mixture of foaming and foam stabilizingsurfactants present in an effective amount.

[0028] A variety of hydraulic cements can be utilized in accordance withthe present invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include, but are not limited to, Portlandcements, pozzolana cements, gypsum cements, aluminous cements, silicacements, and slag cements. Portland cements are generally preferred foruse in accordance with this invention. Portland cements of the typesdefined and described in API Specification For Materials And Testing ForWell Cements, API Specification 10, 5^(th) Edition, dated Jul. 1, 1990of the American Petroleum Institute are particularly suitable. Preferredsuch API Portland cements include classes A, B, C, G and H, with APIclasses G and H being more preferred and class H being the mostpreferred.

[0029] The water utilized in a cement composition of this invention ispresent in a quantity sufficient to produce a pumpable slurry of desireddensity. The water can be fresh water or salt water. The term “saltwater” is used herein to mean unsaturated salt solutions and saturatedsalt solutions including brines and seawater. The water is generallypresent in the cement compositions in an amount in the range of fromabout 35% to about 50% by weight of the cement in the composition.

[0030] As mentioned above, the polymer complex fluid loss controladditive is preferably formed of a cationic, anionic or amphotericpolymer in the presence of a host nonionic polymer. Such polymercomplexes provide excellent fluid loss control in both nonfoamed andfoamed cement compositions over a wide range of temperature and wellconditions. When the polymer complex includes a formed polymer or a hostpolymer of one or more acrylamide type monomers and/or a basicvinylheterocyclic monomer such as vinylimidazole, vinylpyridine,vinylpyrrolidone and their derivatives, the cementing composition mayoptionally include a dispersant such as naphthalene sulfonic acidcondensed with formaldehyde or the condensation reaction product ofacetone, formaldehyde and sodium bisulfite. The inclusion of adispersant has a synergistic affect on the polymer complex which resultsin an unexpected increase in its effectiveness as a fluid loss controladditive.

[0031] When included, the dispersant is present in an amount in therange of from about 0.5% to a maximum about 2% by weight of cement. Adispersant can not be used in foamed cement.

[0032] The various additives conventionally included in cementcompositions which are well known to those skilled in the art can alsobe utilized in the cement compositions of this invention in amountsknown to those skilled in the art.

[0033] The polymer complex fluid loss control additives of thisinvention, when used in a cement composition, effect a substantialreduction in the rate of water loss from the cement composition as wellas in the apparent viscosity of the cement composition. The polymercomplex is easily mixed with the other components of the cementcomposition and results in good fluid loss control over a widetemperature range without affecting rheology adversely. The polymercomplex can be added to a cement composition in dry, solution oremulsion form. The presence of the polymer complex fluid loss controladditive in a cement composition also improves the pumpability of thecement composition.

[0034] As mentioned above, the polymer complex fluid loss controladditive included in a cement composition of this invention ispreferably selected from the group of a polymer complex comprised of 1part by weight of a polymer comprising 70 mole % of2-acrylamido-2-methyl propane sulfonic acid, 17 mole % ofN,N-dimethylacrylamide and 13 mole % of acrylamide, and 2 parts byweight of hydroxyethylcellulose containing 1.5 moles of ethylene oxidesubstitution; or a polymer complex comprised of 1 part by weight of apolymer comprising 40 mole % of 2-acrylamido-2-methyl propane sulfonicacid, 30 mole % of acrylamide, 20 mole % of acrylic acid and 10 mole %of vinylpyrrolidone, and 1 part by weight of hydroxyethylcellulosehaving 1.5 moles of ethylene oxide substitution.

[0035] The polymer complex fluid loss control additive utilized isincluded in the cement composition in an amount in the range of fromabout 0.25% to about 5% by weight of cement in the cement composition.

[0036] When the cement composition is foamed, a gas in an amountsufficient to foam the cement composition and a mixture of foaming andfoam stabilizing surfactants present in an effective amount are includedin the cement composition. The gas utilized for forming the foamedcement composition can be air or nitrogen, with nitrogen beingpreferred.

[0037] The gas is generally present in the cement composition in anamount in the range of from about 10% to about 80% by volume of thefinal foamed cement composition.

[0038] While various mixtures of foaming and foam stabilizingsurfactants can be utilized, a particularly suitable and preferred suchmixture is comprised of an ethoxylated alcohol ether sulfate surfactant,an alkyl or alkene amidopropyl betaine surfactant and an alkyl or alkeneamidopropyldimethylamine oxide surfactant. This surfactant mixture isdescribed in detail in U.S. Pat. No. 6,063,738 issued to Chatterji etal. on May 16, 2000, the disclosure of which is incorporated herein byreference thereto.

[0039] The mixture of foaming and foam stabilizing surfactants ispresent in the cement composition in an effective amount, i.e., in anamount in the range of from about 0.8% to about 5% by volume of water inthe cement composition.

[0040] Another aqueous well treating fluid which can be utilized inaccordance with the methods of this invention is comprised of water, agelling agent present in an amount in the range of from about 0.125% toabout 1.5% by weight of water in the aqueous well treating fluid and awater soluble polymer complex fluid loss control additive present in anamount in the range of from about 0.1% to about 5% by weight of water inthe aqueous well treating fluid.

[0041] The water utilized in the well treating fluid can be fresh wateror salt water as described above.

[0042] One or more gelling agents for increasing the viscosity of theaqueous treating fluid are included therein. The increased viscosity ofthe treating fluid allows the treating fluid to carry particulate solidmaterials and deposit the particulate solid materials in a desiredlocation. For example, when the viscous gelled aqueous treating fluid isutilized as a fracturing fluid, it is pumped into a subterranean zone byway of the well bore at a rate and pressure sufficient to fracture thesubterranean zone. The viscous fracturing fluid carries particulateproppant material such as graded sand into the fractures. The proppantmaterial is suspended in the viscous fracturing fluid so that theproppant material is deposited in the fractures when the viscousfracturing fluid is broken (reverts to a thin fluid) and recovered. Theproppant material functions to prevent the fractures from closingwhereby conductive channels are formed through which produced fluids canflow to the well bore.

[0043] A viscous gelled aqueous treating fluid is also utilized ingravel packing. In gravel packing operations, solid gravel particles,such as graded sand or the like, are carried into a subterranean zonecontaining a screen within which a gravel pack is to be placed by theviscous aqueous treating fluid. That is, the gravel is suspended in theviscous aqueous treating fluid at the surface and carried into a spacebetween the screen and the walls of the well bore penetrating thesubterranean zone within which the gravel pack is to be placed. Once thegravel is placed in the zone, the viscous gelled fluid is broken (theviscosity is reduced) and recovered (returned to the surface). Thegravel pack functions as a filter to separate formation solids fromproduced fluids while permitting the produced fluids to flow into andthrough the well bore.

[0044] A variety of gelling agents can be utilized to increase theviscosity of aqueous well treating fluids such as fracturing fluids,gravel packing fluids and the like. The useful gelling agents includenatural and derivatized polysaccharides which are soluble, dispersibleor swellable in an aqueous liquid to yield viscosity to the liquid. Onegroup, for example, of polysaccharides which are suitable for use inaccordance with the present invention includes, but is not limited to,galactomannan gums such as gum arabic, gum ghatti, gum karaya, tamarindgum, tragacanth gum, guar gum, locust bean gum, and the like. The gumscan also be characterized as having one or more functional groups suchas cis-hydroxyl, hydroxyl, carboxyl, sulfate, sulfonate, amino or amide.Modified gums such as carboxyalkyl derivatives, e.g., carboxymethylguarand hydroxyalkyl derivatives, e.g., hydroxypropylguar can also beemployed. Doubly derivatized gums such as carboxymethylhydroxypropylguarcan also be used.

[0045] Modified celluloses and derivatives thereof can also be employedin accordance with the present invention. Examples of water-solublecellulose ethers which can be used include, but are not limited to,carboxyethylcellulose, carboxymethylcellulose,carboxymethylhydroxyethylcellulose, hydroxyethylcellulose,methylhydroxypropylcellulose, methylcellulose, ethylcellulose,ethylcarboxymethylcellulose, methylethylcellulose,hydroxypropylmethylcellulose and the like. A particularly suitablederivatized cellulose is hydroxyethylcellulose grafted with vinylphosphonic acid which is described in detail in U.S. Pat. No. 5,067,565issued to Holtmyer et al. on Nov. 26, 1991, the disclosure of which isincorporated herein by reference thereto.

[0046] Of the galactomannans and derivative galactomannans, guar gum,hydroxypropylguar, carboxymethylhydroxypropylguar,hydroxyethylcellulose, carboxymethylhydroxyethylcellulose,carboxymethylcellulose, hydroxyethylcellulose grafted with vinylphosphonic acid are preferred.

[0047] Various other gelling agents known to those skilled in the artincluding biopolymers such as xanthan gum, welan gum and succinoglyconcan also be used. The gelling agent or agents utilized are included inthe aqueous well treating fluids of this invention in an amount in therange of from about 0.125% to about 1.5% by weight of water in thetreating fluid.

[0048] In order to further enhance the development of viscosity of theaqueous well treating fluid containing the above polysaccharide gellingagents, the gelling agents can be cross-linked by the addition of across-linking agent to the aqueous treating fluid. The cross-linkingagent can comprise a borate releasing compound or any of the well knowntransition metal ions which are capable of creating a cross-linkedstructure with the particular gelling agent utilized. Preferredcross-linking agents for use with the above described gelling agentsinclude, but are not limited to, borate releasing compounds, a source oftitanium ions, a source of zirconium ions, a source of antimony ions anda source of aluminum ions.

[0049] When used, a cross-linking agent of the above types is includedin the aqueous well treating fluid in an amount in the range of fromabout 0.1% to about 2% by weight of gelling agent in the treating fluid.

[0050] When the aqueous well treating fluid includes a gelling agent ora cross-linked gelling agent, a delayed breaker for the gelling agent orcross-linked gelling agent is included in the aqueous well treatingfluid. That is, the delayed breaker is included in the aqueous treatingfluid in an amount sufficient to effect a controlled reduction in theviscosity of the aqueous treating fluid after a desired period of time.Suitable delayed breakers which can be utilized include alkali metal andammonium persulfates which are delayed by being encapsulated in amaterial which slowly releases the breaker. Such a material isprecipitated particulate silica which is porous and remains dry and freeflowing after absorbing an aqueous solution of the breaker. Precipitatedsilica can absorb chemical additive solutions in amounts up to about400% by weight of the precipitated silica. The delayed release of aliquid chemical additive absorbed in a particulate porous precipitatedsilica is by osmosis whereby the encapsulated liquid chemical diffusesthrough the porous solid material as a result of it being at a higherconcentration within the porous material than its concentration in theliquid fluid outside the porous material. In order to further delay therelease of a liquid chemical additive, the porous precipitated silicacan be coated with a slowly soluble coating. Examples of suitable suchslowly soluble materials which can be used include, but are not limitedto, EDPM rubber, polyvinyldichloride (PVDC), nylon, waxes,polyurethanes, cross-linked partially hydrolyzed acrylics and the like.A detailed description of the encapsulating techniques described aboveis set forth in U.S. Pat. No. 6,209,646 issued on Apr. 3, 2001 to Reddyet al., the disclosure of which is incorporated herein by referencethereto. Other delayed breakers which can be utilized include, but arenot limited to, alkali metal chlorides and hypochlorites and calciumhypochlorites.

[0051] When used, a breaker of the above types is included in theaqueous well treating fluid in an amount in the range of from about0.01% to about 5% by weight of water in the treating fluid.

[0052] As mentioned above, the polymer complex fluid loss controladditives which are useful in accordance with the methods of the presentinvention are made by polymerizing a cationic, anionic or amphotericpolymer in the presence of a nonionic host polymer. The monomers whichcan be utilized in the polymerization of the cationic, anionic oramphoteric polymer are those that promote water solubility including,but not limited to, monomers such as 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropane sulfonic acid,sulfonated styrene, vinyl sulfonic acid, allyl ether sulfonic acids suchas propane sulfonic acid allyl ether, methallyl ether phenyl sulfonates,acrylic acid, methacrylic acid, maleic acid, itaconic acid,n-acrylamidopropyl-n,n-dimethyl amino acid,n-methacrylamidopropyl-n,n-dimethyl amino acid,n-acryloyloxyethyl-n,n-dimethyl amino acid,n-methacryloyloxyethyl-n,n-dimethyl amino acid,n-acryloyloxyethyl-n,n-dimethyl amino acid,n-methacryloyloxyethyl-n,n-dimethyl amino acid, crotonic acid,acrylamidoglycolic acid, methacrylamidoglycolic acid,2-acrylamido-2-methylbutanoic acid and 2-methacrylamido-2-methylbutanoicacid. Nonionic monomers which can be used in the formed (synthesized)polymer include, but are not limited to, C₁-C₂₂ straight or branchedchain alkyl or aryl acrylamide, C₁-C₂₂ straight or branched chainn-alkyl or aryl methacrylamide, acrylamide, methacrylamide,n-vinylpyrrolidone, vinyl acetate, ethoxylated and propoxylatedacrylate, ethoxylated and propoxylated methacrylate, hydroxy functionalacrylates such as hydroxyethylacrylate and hydroxypropylacrylate,hydroxy functional methacrylates such as hydroxyethylmethacrylate andhydroxypropylmethacrylate, n,n-dimethylacrylamide,n,n-dimethylmethacrylamide, styrene, styrene derivatives and C₁-C₂₂straight or branched chain alkyl, aryl or allyl ethers.

[0053] The polymer complexes of the present invention are formed bypolymerizing one or more of the above described monomers in the presenceof a nonionic host polymer. The host polymer can be a synthetic polymer,such as those produced by free radical polymerization or condensationpolymerization or it can be a natural polymer such as a natural gum, anatural gum derivative, a starch, a modified starch, a cellulose, acellulose derivative or an ethoxylated cellulose derivative. Otherpolymers that can be used include, but are not limited to, vinylpolymers, polyolefins, polyacrylates, polyamides, polyesters,polyurethanes, xanthan gums, welan gums, succinoglycon, sodiumalginates, galactomannans, carragenan, gum arabic, starch and itsderivatives, guar ester derivatives, silicone containing polymers andtheir derivatives, polysiloxanes and their derivatives and proteins andtheir derivatives.

[0054] The term “interjacent” can be used to describe the polymercomplexes useful in accordance with this invention. By interjacent, itis meant that the polymers of the polymer complex are distributedhomogeneously throughout the composition and intermingled to a degreethat no visible phase separation will be observed after standing in theoriginal solution for a long period of time. On the other hand, athree-dimensional network structure is also substantially absent(although there may be some branching), so that a solution manifestsonly a very minimal turbidity, if any. As a non-limiting example, anaqueous solution containing 5 percent by weight of a polymer orinterjacent complex can be prepared and poured through a U.S. StandardSieve No. 100 (150 μm) and no particles are left on the screen.Alternatively, a 2.5% by weight solution of the polymer complexes orinterjacent polymer complexes of the present invention will have aturbidity reading of less than 20 nephelometric turbidity units (NTU's)and no visible phase separation after standing at ambient conditions forthree months occurs.

[0055] Additional information concerning the preparation and make-up ofthe polymer complex fluid loss control additives of this invention isincluded in U.S. patent application Ser. No. ______ entitled WaterSoluble Polymer Complexes In Cementing filed on Apr. 15, 2002, thedisclosure of which is incorporated herein by reference thereto. Also,additional information concerning the polymer complex fluid loss controlagents of this invention is disclosed in Provisional Application SerialNo. 60/284,043 entitled Water Soluble Polymer Complexes filed on Apr.16, 2001, the disclosure of which is incorporated herein by referencethereto.

[0056] In order to further illustrate the methods of the presentinvention, the following examples are given.

EXAMPLE 1

[0057] A monomer mixture was prepared containing 0.0043 grams ofmethylene bis-acrylamide, 28.27 grams of 2-acrylamido-2-methylpropanesulfonic acid, 1.79 grams of acrylamide, 4.97 grams of ammoniumchloride, 3.28 grams of N,N-dimethylacrylamide, 0.04 grams of thetetrasodium salt of ethylenediaminetetraacetic acid, 10.93 grams of a50% sodium hydroxide solution, and 0.83 grams of a 50% aqueous solutionof 2-mercaptoethanol. The mixture was added to a polymerization kettlecontaining 851.49 grams of deionized water. The pH of the resultingsolution was above 8.5. The mixture was continuously agitated, heated to118° F. and 0.67 grams of 2,2′-azobis(2-amidinopropane) hydrochlorideinitiator was added to the solution. 66.67 grams ofhydroxyethylcellulose having 1.5 moles of ethylene oxide substitutionwere added to the agitated solution and the hydroxyethylcellulose wasallowed to undergo complete hydration therein. A nitrogen sparge in thepolymerization kettle was started and polymerization was allowed toproceed adiabatically. After a heat rise in the polymerization mixturestopped, the mixture was heated to 150° F. followed by the addition of0.33 grams of 2,2′-azobis(2-amidinopropane) hydrochloride initiatordissolved in 1.33 grams of deionized water. The resulting solution wasmaintained at 150° F. for 30 minutes, allowed to cool and a 10% activesolution of the polymer complex produced was collected.

[0058] The polymer complex produced consisted of 1 part by weight of thesynthesized polymer containing 70 mole % of 2-acrylamido-2-methylpropanesulfonic acid, 17 mole % of N,N-dimethylacrylamide and 13 mole % ofacrylamide, and 2 parts by weight of hydroxyethylcellulose having 1.5moles of ethylene oxide substitution. This polymer complex wasdesignated 2004-72.

[0059] Following the above described polymerization process, a differentpolymer complex was prepared consisting of 1 part by weight of asynthesized polymer containing 40 mole % of 2-acrylamido-2-methylpropanesulfonic acid, 30 mole % of acrylamide, 20 mole % of acrylic acid and 10mole % of vinylpyrrolidone, and 1 part by weight hydroxyethylcellulosehaving 1.5 moles of ethylene oxide substitution. This polymer complexwas designated 2004-96.

[0060] Following the same polymerization process described above, asynthesized polymer was prepared without the host polymer, i.e.,hydroxyethylcellulose with 1.5 moles of ethylene oxide substitution. Thesynthesized polymer consisted of 40 mole % of2-acrylamido-2-methylpropane sulfonic acid, 30 mole % of acrylamide, 20mole % of acrylic acid and 10 mole % of vinylpyrrolidone. This syntheticpolymer without the host polymer was designated 2004-97.

[0061] A cement slurry was prepared comprised of Lafarge Class HPortland cement, 30% of silica flour by weight of cement, 15% of fumedsilica by weight of cement, 1% of a non-dispersing set retarder byweight of cement, 46.5% water by weight of cement and 2% of a mixture offoaming and foam stabilizing surfactants by volume of the water. Thenon-dispersing set retarder was comprised of a mixture oflignosulfonate, sugar and sulfonated lignin. The set retarder isdescribed in detail in U.S. Pat. No. 6,227,294 B1 issued to Chatterji etal. on May 8, 2001, the disclosure of which is incorporated herein byreference thereto. The mixture of foaming and foam stabilizingsurfactant was comprised of an ethoxylated alcohol ether sulfatesurfactant, an alkyl or alkene amidopropylbetaine surfactant and analkyl or alkene amidopropyldimethylamine oxide surfactant. The densityof the cement slurry was 16.1 pounds per gallon. The three fluid losscontrol additives designated as 2004-72, 2004-96 and 2004-97 were addedto separate portions of the above described cement slurry in the amountsgiven in Table I below. Thereafter, the test cement slurried were foamedand then tested for fluid loss in accordance with the API SpecificationFor Materials And Testing For Well Cements referred to above using aMultiple Analysis Cement Slurry Analyzer (MACS). The MACS analyzerincludes a sealable chamber having a known volume where a cement slurryis sheared at high energy while being pressurized and heated. The testcement slurries containing the fluid loss control additives were eachplaced in a standard 2-liter Waring blender. The weight of each of thecement slurries was 1,829.84 grams to which was added 10.69 grams of themixture of foaming and foam stabilizing surfactants described above.After mixing in the Waring blender, each of the cement slurries wasseparately placed into the MACS chamber. The amount of each cementslurry utilized was predetermined to result in the desired foamed slurrydensity when the slurry was foamed sufficiently to completely fill thechamber of the MACS analyzer. After each cement slurry was placed in theMACS chamber, the chamber was sealed and the paddle inside the analyzerwas rotated at approximately 1,000 RPM for 5 minutes with 1,000 psinitrogen pressure applied to the cement slurry. As a result, the cementslurry in the chamber was converted to a test foamed cement compositionhaving a density of 12 pounds per gallon. After being foamed, the testfoamed cement composition was subjected to a temperature schedule whichsimulates well conditions while maintaining pressure on the foamedcement composition. After reaching the maximum temperature equivalent tothe bottom hole circulating temperature (BHCT) of a well, the stirringof the test foamed cement composition was continued for 1 hour. The testfoamed cement composition was then transferred through a specialmanifold system to a special fluid loss cell or to curing cells thatwere preheated and charged with nitrogen to the same pressure as thetest foamed cement composition. By venting the nitrogen pressure fromthe fluid loss cell or curing cells, the test foamed cement compositionwas transferred from the analyzer chamber into the fluid loss cell orcuring cells. When the test foamed cement composition was transferred tothe fluid loss cell, the liquid effluents from the foamed cementcomposition were collected to determine the fluid loss controlproperties of the test foamed cement composition. The fluid loss testresults are given in Table I below. In order to determine the stabilityof the test foamed cement composition, a portion of the test foamedcement composition was transferred to the curing cells. The cells werethen subjected to the bottom hole static temperature (BHST) for curing.Upon the completion of curing, the nitrogen pressure was slowly releasedfrom the curing cells. The set foamed cement composition was thenremoved from the cells and tested for compressive strength. The resultsof these tests are also given in Table I below. TABLE I Fluid Loss AndCompressive Strength Results Fluid Loss Quantity of Fluid Loss FoamCompressive Control Additive Control Additive, % Fluid Loss, cc/30 minStability at Strength of Foam Designation by wt. of cement 160° F. 250°F. 275° F. 12 lb/gal After Setting, psi 2004-72 1.0 22 — — Stable 11342004-72 1.0  30¹ — — 2004-72 1.5 — 24 — 2004-72 1.5 — — 29 2004-96 1.016 — — Stable 503 2004-96 1.5 — 28 — 2004-96 1.5 — — 32 2004-97 1.0 116 — — Stable 753

[0062] From Table I it can be seen that the test foamed cementcompositions containing the polymer complex fluid loss control additives2004-72 and 2004-96 exhibited exceptional fluid loss control in therange of 100-275° F. bottom hole circulating temperatures (BHCT). Thecement composition containing the polymer 2004-97 (without a hostpolymer) exhibited high fluid loss. All of the test foamed cementcompositions were stable and had good compressive strengths.

EXAMPLE 2

[0063] A portion of the cement slurry designated 2004-72 was foamed inthe MACS Analyzer as described in Example 1 above. The cement slurry wasfoamed to a density of 12 pounds per gallon at 80° F. and 1,000 psi. Thetemperature of the foamed cement composition was then gradually raisedat a rate of 2.5° F. per minute to 250° F. and held at 250° F. for 1hour. The foamed cement composition was then transferred to the curingcells which were preheated to 250° F. The curing cells were charged withnitrogen at 1,000 psi. The foamed cement composition in one cell had adensity of 11.77 pounds per gallon and in the other cell 11.76 poundsper gallon before setting. The cells were then cured at 318° F. and1,000 psi for 24 hours. The set foamed cement composition in the curingcells were removed therefrom and cooled to room temperature at ambientpressure. The set foamed cement compositions were each cut into 3sections; top, middle and bottom and the average densities of thesections were determined. The results of these tests are given in TableII below. TABLE II Densities Of Set Samples Cell 1 Density, lb/gal Cell2 Density, lb/gal Top Middle Bottom Top Middle Bottom 11.77 12.15 12.6211.65 12.13 12.96

[0064] From Table II it can be seen that the average density of the topsection was 11.71 pounds per gallon; the middle section was 12.14 poundsper gallon and the bottom section was 12.79 pounds per gallon. Thus, thedensity variation in the cured samples from top to bottom did not exceed1 pound per gallon. This result indicates that the polymer complex fluidloss control additive utilized in accordance with this invention isnon-dispersing.

EXAMPLE 3

[0065] Portions of the cement slurries described in Example 1 werefoamed as described in Example 1 to densities of 12 pounds per gallon.The foamed cement compositions were tested for thickening times inaccordance with the procedures set forth in the API Specification 10referred to above. The results of the thickening time tests are setforth in Table III below. TABLE III Thickening Time Results Quantity ofFluid Loss Fluid Loss Quantity of Quantity of Quantity of ControlControl Silica Flour, % Fumed Silica, Surfactants, Thickening AdditiveAdditive, % by by wt. of % by wt. of % by wt. of Temp., Time,Designation wt. of Cement Cement Cement Water ° F. hr:min 2004-72 1.0 35— — 250 6:21  2004-72 1.0 30 15 1 250 4:24  2004-96 1.0 35 — — 300 6:00+

[0066] From Table III it can be seen that the foamed cement compositionscontaining the polymer complex fluid loss control additive had goodthickening times.

[0067] Thus, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thoseinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. A method of treating a subterranean zonepenetrated by a well bore comprising introducing into said subterraneanzone an aqueous well treating fluid comprised of water and a watersoluble polymer complex fluid loss control additive.
 2. The method ofclaim 1 wherein said water soluble polymer complex fluid loss controladditive is comprised of a cationic, anionic or amphoteric polymerformed in the presence of a nonionic host polymer.
 3. The method ofclaim 2 wherein the weight ratio of said cationic, anionic or amphotericpolymer to said nonionic polymer is in the range of from about 1:10 toabout 10:1.
 4. The method of claim 2 wherein said nonionic polymer is anatural gum.
 5. The method of claim 2 wherein said nonionic polymer is ahydroxyalkylated natural gum.
 6. The method of claim 2 wherein saidnonionic polymer is hydroxyethylcellulose having 1.5 moles of ethyleneoxide substitution.
 7. The method of claim 2 wherein the monomer unitsforming said cationic, anionic or amphoteric polymer are comprised ofmonomer units derived from a sulfonic acid functional monomer.
 8. Themethod of claim 2 wherein the monomer units forming said cationic,anionic or amphoteric polymer are comprised of 2-acrylamido-2-methylpropane sulfonic acid monomer units present in said polymer in an amountin the range of from about 25 mole % to about 75 mole %.
 9. The methodof claim 8 wherein the monomer units forming said cationic, anionic oramphoteric polymer are further comprised of N,N-dimethylacrylamidemonomer units present in said polymer in an amount in the range of fromabout 10 mole % to about 40 mole %.
 10. The method of claim 8 whereinthe monomer units forming said cationic, anionic or amphoteric polymerare further comprised of acrylamide monomer units present in saidpolymer in an amount in the range of from about 10 mole % to about 30mole %.
 11. The method of claim 8 wherein the monomer units forming saidcationic, anionic or amphoteric polymer are further comprised of acrylicacid monomer units present in said polymer in an amount in the range offrom about 10 mole % to about 20 mole %.
 12. The method of claim 8wherein the monomer units forming said cationic, anionic or amphotericpolymer are further comprised of vinyl pyrrolidone monomer units presentin said polymer in an amount in the range of from about 5 mole % toabout 20 mole %.
 13. The method of claim 1 wherein said water solublepolymer complex fluid loss control additive is comprised of 1 part byweight of a polymer comprised of 70 mole % of 2-acrylamido-2-methylpropane sulfonic acid, 17 mole % of N,N-dimethylacrylamide and 13 mole %of acrylamide and 2 parts by weight of a nonionic polymer comprised ofhydroxyethylcellulose having 1.5 moles of ethylene oxide substitution.14. The method of claim 1 wherein said water soluble polymer complexfluid loss control additive is comprised of 1 part by weight of apolymer comprised of 40 mole % of 2-acrylamido-2-methyl propane sulfonicacid, 30 mole % of acrylamide, 20 mole % of acrylic acid and 10 mole %of vinyl pyrrolidone and 1 part by weight of a nonionic polymercomprised of hydroxyethylcellulose having 1.5 moles of ethylene oxidesubstitution.
 15. The method of claim 1 wherein said water solublepolymer complex fluid loss control additive is present in said aqueouswell treating fluid in an amount in the range of from about 0.09% toabout 2.5% by weight of water in said well treating fluid.
 16. Themethod of claim 1 wherein said aqueous well treating fluid furthercomprises a hydraulic cement.
 17. The method of claim 16 wherein saidhydraulic cement is a Portland cement.
 18. The method of claim 16wherein said water is present in said aqueous well treating fluid in anamount in the range of from about 35% to about 50% by weight of cementin said treating fluid.
 19. The method of claim 16 wherein said aqueouswell treating fluid further comprises a gas in an amount sufficient tofoam said aqueous well treating fluid and a mixture of foaming and foamstabilizing surfactants present in an effective amount.
 20. The methodof claim 19 wherein said gas is selected from the group of air andnitrogen.
 21. The method of claim 19 wherein said gas is nitrogen. 22.The method of claim 19 wherein said mixture of foaming and foamstabilizing surfactants is comprised of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactantand an alkyl or alkene amidopropyl dimethyl amine oxide surfactant. 23.The method of claim 19 wherein said mixture of foaming and foamstabilizing surfactants is present in said aqueous well treating fluidin an amount in the range of from about 0.8% to about 5% by volume ofwater in said treating fluid.
 24. The method of claim 1 wherein saidaqueous well treating fluid further comprises a gelling agent forincreasing the viscosity of said fluid.
 25. The method of claim 24wherein said gelling agent is selected from the group consisting of guargum, hydroxypropylguar, carboxymethylhydroxypropyl guar,hydroxyethylcellulose, carboxymethylhydroxyethylcellulose,carboxymethylcellulose, hydroxyethylcellulose grafted with vinylphosphonic acid, xanthan gum, welan gum and succinoglycon.
 26. Themethod of claim 24 wherein said gelling agent is present in said aqueouswell treating fluid in an amount in the range of from about 0.125% toabout 1.5% by weight of water in said treating fluid.
 27. The method ofclaim 24 wherein said aqueous well treating fluid further comprises across-linking agent for cross-linking said gelling agent.
 28. The methodof claim 27 wherein said cross-linking agent is selected from the groupconsisting of borate releasing compounds, a source of titanium ions, asource of zirconium ions, a source of antimony ions and a source ofaluminum ions.
 29. The method of claim 27 wherein said cross-linkingagent is present in said aqueous well treating fluid in an amount in therange of from about 0.1% to about 2% by weight of said gelling agent insaid treating fluid.
 30. The method of claim 24 or 27 wherein saidaqueous well treating fluid further comprises a delayed breaker presentin an amount sufficient to effect a reduction in the viscosity of saidtreating fluid after said treating fluid has been in said subterraneanzone for a period of time.
 31. The method of claim 30 wherein saiddelayed breaker is selected from the group consisting of alkali metaland ammonium persulfates which are delayed by being encapsulated in amaterial which slowly releases said breaker or by a breaker selectedfrom the group consisting of alkali metal chlorites, alkali metalhypochlorites and calcium hypochlorites.
 32. A method of cementing asubterranean zone penetrated by a well bore comprising introducing intosaid subterranean zone a cement composition comprised of a hydrauliccement slurried with water and a water soluble polymer complex fluidloss control additive present in an amount in the range of from about0.25% to about 5% by weight of cement in said composition.
 33. Themethod of claim 32 wherein said water soluble polymer complex fluid losscontrol additive is comprised of an cationic, anionic or amphotericpolymer formed in the presence of a nonionic host polymer.
 34. Themethod of claim 33 wherein the weight ratio of said cationic, anionic oramphoteric polymer to said nonionic host polymer is in the range of fromabout 1:10 to about 10:1.
 35. The method of claim 33 wherein saidnonionic polymer is a natural gum.
 36. The method of claim 33 whereinsaid nonionic polymer is a hydroxyalkylated natural gum.
 37. The methodof claim 33 wherein said nonionic polymer is hydroxyethylcellulosehaving 1.5 moles of ethylene oxide substitution.
 38. The method of claim33 wherein the monomer units forming said polymer are comprised ofmonomer units derived from a sulfonic acid functional monomer.
 39. Themethod of claim 33 wherein the monomer units forming said polymer arecomprised of 2-acrylamido-2-methyl propane sulfonic acid monomer unitspresent in said polymer in an amount in the range of from about 25 mole% to about 75 mole %.
 40. The method of claim 39 wherein the monomerunits forming said polymer are further comprised ofN,N-dimethylacrylamide monomer units present in said polymer in anamount in the range of from about 10 mole % to about 40 mole %.
 41. Themethod of claim 39 wherein the monomer units forming said polymer arefurther comprised of acrylamide monomer units present in said polymer inan amount in the range of from about 10 mole % to about 30 mole %. 42.The method of claim 39 wherein the monomer units forming said cationic,anionic or amphoteric polymer are further comprised of acrylic acidmonomer units present in said polymer in an amount in the range of fromabout 10 mole % to about 20 mole %.
 43. The method of claim 39 whereinthe monomer units forming said polymer are further comprised of vinylpyrrolidone monomer units present in said polymer in an amount in therange of from about 5 mole % to about 20 mole %.
 44. The method of claim32 wherein said water soluble polymer complex fluid loss controladditive is comprised of 1 part by weight of a polymer comprised of 70mole % of 2-acrylamido-2-methyl propane sulfonic acid, 17 mole % ofN,N-dimethylacrylamide and 13 mole % of acrylamide and 2 parts by weightof a nonionic polymer comprised of hydroxyethylcellulose having 1.5moles of ethylene oxide substitution.
 45. The method of claim 32 whereinsaid water soluble polymer complex fluid loss control additive iscomprised of 1 part by weight of a polymer comprised of 40 mole % of2-acrylamido-2-methyl propane sulfonic acid, 30 mole % of acrylamide, 20mole % of acrylic acid and 10 mole % of vinyl pyrrolidone and 1 part byweight of a nonionic polymer comprised of hydroxyethylcellulose having1.5 moles of ethylene oxide substitution.
 46. The method of claim 32wherein said water is present in said cement composition in an amount inthe range of from about 35% to about 50% by weight of cement in saidcement composition.
 47. The method of claim 32 wherein said cementcomposition further comprises a dispersant selected from the groupconsisting of naphthalene sulfonic acid condensed with formaldehyde andthe condensation reaction product of acetone, formaldehyde and sodiumbisulfite present in an amount in the range of from about 0.5% to 2% byweight of cement in said composition.
 48. The method of claim 32 whereinsaid cement composition further comprises a gas in an amount sufficientto foam said cement composition and a mixture of foaming and foamstabilizing surfactants present in an effective amount.
 49. The methodof claim 48 wherein said gas is selected from the group of air andnitrogen.
 50. The method of claim 48 wherein said gas is nitrogen. 51.The method of claim 48 wherein said mixture of foaming and foamstabilizing surfactants is comprised of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactantand an alkyl or alkene amidopropyl dimethyl amine oxide surfactant. 52.The method of claim 48 wherein said mixture of foaming and foamstabilizing surfactants is present in said cement composition in anamount in the range of from about 0.8% to about 5% by volume of water insaid treating fluid.
 53. A method of treating a subterranean zonepenetrated by a well bore comprising introducing into said subterraneanzone an aqueous well treating fluid comprised of water, a gelling agentpresent in an amount in the range of from about 0.125% to about 1.5% byweight of water in said aqueous well treating fluid and a water solublepolymer complex fluid loss control additive present in an amount in therange of from about 0.1% to about 5% by weight of water in said aqueouswell treating fluid.
 54. The method of claim 53 wherein said watersoluble polymer complex fluid loss control additive is comprised of ancationic, anionic or amphoteric polymer formed in the presence of anonionic host polymer.
 55. The method of claim 54 wherein the weightratio of said cationic, anionic or amphoteric polymer to said nonionicpolymer is in the range of from about 1:10 to about 10:1.
 56. The methodof claim 54 wherein said nonionic polymer is a natural gum.
 57. Themethod of claim 54 wherein said nonionic polymer is a hydroxyalkylatednatural gum.
 58. The method of claim 54 wherein said nonionic polymer ishydroxyethylcellulose having 1.5 moles of ethylene oxide substitution.59. The method of claim 54 wherein the monomer units forming saidpolymer are comprised of monomer units derived from a sulfonic acidfunctional monomer.
 60. The method of claim 54 wherein the monomer unitsforming said polymer are comprised of 2-acrylamido-2-methyl propanesulfonic acid monomer units present in said polymer in an amount in therange of from about 25 mole % to about 75 mole %.
 61. The method ofclaim 60 wherein the monomer units forming said polymer are furthercomprised of N,N-dimethylacrylamide monomer units present in saidpolymer in an amount in the range of from about 10 mole % to about 40mole %.
 62. The method of claim 60 wherein the monomer units formingsaid polymer are further comprised of acrylamide monomer units presentin said polymer in an amount in the range of from about 10 mole % toabout 30 mole %.
 63. The method of claim 60 wherein the monomer unitsforming said polymer are further comprised of acrylic acid monomer unitspresent in said polymer in an amount in the range of from about 10 mole% to about 20 mole %.
 64. The method of claim 60 wherein the monomerunits forming said polymer are further comprised of vinyl pyrrolidonemonomer units present in said polymer in an amount in the range of fromabout 5 mole % to about 20 mole %.
 65. The method of claim 53 whereinsaid water soluble polymer complex fluid loss control additive iscomprised of 1 part by weight of a polymer comprised of 70 mole % of2-acrylamido-2-methyl propane sulfonic acid, 17 mole % ofN,N-dimethylacrylamide and 13 mole % of acrylamide and 2 parts by weightof a nonionic polymer comprised of hydroxyethylcellulose having 1.5moles of ethylene oxide substitution.
 66. The method of claim 53 whereinsaid water soluble polymer complex fluid loss control additive iscomprised of 1 part by weight of a polymer comprised of 40 mole % of2-acrylamido-2-methyl propane sulfonic acid, 30 mole % of acrylamide, 20mole % of acrylic acid and 10 mole % of vinyl pyrrolidone and 1 part byweight of a nonionic polymer comprised of hydroxyethylcellulose having1.5 moles of ethylene oxide substitution.
 67. The method of claim 53wherein said gelling agent is selected from the group consisting of guargum, hydroxypropylguar, carboxymethylhydroxypropyl guar,hydroxyethylcellulose, carboxymethylhydroxyethylcellulose,carboxymethylcellulose, hydroxyethylcellulose grafted with vinylphosphonic acid, xanthan gum, welan gum and succinoglycon.
 68. Themethod of claim 53 wherein said gelling agent is present in said aqueouswell treating fluid in an amount in the range of from about 0.125% toabout 1.5% by weight of water in said treating fluid.
 69. The method ofclaim 53 wherein said aqueous well treating fluid further comprises across-linking agent for cross-linking said gelling agent.
 70. The methodof claim 69 wherein said cross-linking agent is selected from the groupconsisting of borate releasing compounds, a source of titanium ions, asource of zirconium ions, a source of antimony ions and a source ofaluminum ions.
 71. The method of claim 69 wherein said cross-linkingagent is present in said aqueous well treating fluid in an amount in therange of from about 0.1% to about 2% by weight of said gelling agent insaid treating fluid.
 72. The method of claim 53 or 69 wherein saidaqueous well treating fluid further comprises a delayed breaker presentin an amount sufficient to effect a reduction in the viscosity of saidtreating fluid after said treating fluid has been in said subterraneanzone for a period of time.
 73. The method of claim 72 wherein saiddelayed breaker is selected from the group consisting of alkali metaland ammonium persulfates which are delayed by being encapsulated in amaterial which slowly releases said breaker or by a breaker selectedfrom the group consisting of alkali metal chlorites, alkali metalhypochlorites and calcium hypochlorites.